TNU-9, a new zeolite for the selective catalytic reduction of NO: An in situ X-ray absorption spectroscopy study

The medium-pore zeolite TNU-9 was prepared and studied for the selective catalytic reduction (SCR) of NO using C3H8 as the reducing agent. The catalytic activities of copper- and cobalt-exchanged TNU-9 zeolites are compared with those of other active metal-exchanged zeolites previously studied, such as Cu- and Co-Beta, IM-5, and ZSM-5. The catalytic results obtained on TNU-9 zeolites at different oxygen content and different temperatures are similar to those observed with the other known highly active zeolites but with the advantage of TNU-9 having almost the same catalytic performance in the presence of H2O during the reaction. The nature and behavior of Cu and Co active sites contained in the TNU-9 catalysts have been studied under operating conditions using X-ray absorption spectroscopy. After catalyst activation at 550 °C under He, mostly reduced Cu1+ and Co2−x species are detected. Nevertheless, the activated catalysts show a very low reaction rate for the SCR of NOx in the absence of O2. However, when O2 is introduced into the reaction stream, a mixed-valence system is observed, as well as an important increase in the catalytic reaction rate. The results obtained show that the presence of metal sites having different oxidation states in the catalyst is mandatory for obtaining good results in the NOx SCR reaction.